1. Field of the Disclosure
This disclosure relates to an electrophoretic display device, and more particularly to a configurationally simplified electrophoretic display device.
2. Description of the Related Art
Nowadays, flexible display devices have been developed which do not damage upon folding or rolling. These flexible display devices include the existing flat display devices, such as pliable LCD (liquid crystal display) and OLED (organic electro-luminescent display) devices, as well as electro-paper devices such as electrophoretic display devices.
Among these flexible display devices, the electrophoretic display device uses an electrophoresis phenomenon which allows charged particles (or leptons) to move toward an anode electrode or a cathode electrode within an electric field. This eliminates the necessity of an internal light source. In other words, the electrophoretic display device may be a reflective display device which drives electrophoretic suspension particles (or leptons) using transparent conductive films coated on flexible thin base films such as a metal film or a plastic sheet. As such, the electrophoretic display device has features such as a reflectivity corresponding to paper, a superior readability based on a wide viewing angle, good pliability and portability, is slim, and has a light-weight size. In view of this, the electrophoretic display device has received a growing amount of attention as a next-generation display device and as an electro-paper.
FIG. 1 is a cross-sectional view showing one pixel included in an electrophoretic display device of related art. As shown in FIG. 1, the electrophoretic display device includes an electrophoretic film 30, an insulation film 33, and an upper substrate 10 sequentially stacked on a lower substrate 50. The lower substrate 50 includes a first base substrate 51 and lower electrodes 52 to 54 formed on the first base substrate 51. The insulation film 33 includes a common electrode 31 formed on its lower surface. The upper substrate 10 includes a second base substrate 11 and red, green, and blue color filters 12 to 14 formed on the second base substrate 11. The electrophoretic film 30 includes a polymer containing electronic ink capsules. Each electronic ink capsule consists of white ink and black ink.
Such an electrophoretic display device applies an arbitrary polarity voltage to the lower electrodes 52 to 54 on the lower substrate 50 and a common voltage to the common electrode 31. In accordance therewith, the white ink and the black ink are separated from each other by an electric field between the lower electrodes 52 to 54 and the common electrode 31.
If a negative polarity voltage is applied to the lower electrodes 52 to 54, the common voltage on the common electrode 31 becomes a positively-charged electric potential opposite to the negative polarity voltage. Then, the positively-charged white ink moves toward the lower substrate 50, while the negatively-charged black ink moves toward the upper substrate 10.
In contrast, when a positive polarity voltage is applied to the lower electrodes 52 to 54, the common voltage on the common electrode 31 becomes a negatively-charged electric potential opposite to the positive polarity voltage. In this case, the negatively-charged white ink moves toward the upper substrate 10, while the positively-charged black ink moves toward the lower substrate 50.
In this way, the electrophoretic display device moves the white ink toward the upper substrate 10 by applying the positive polarity voltage to the lower electrodes 52 to 54 and the moved white ink is able to reflect light from the exterior toward the upper substrate 10. The reflected light restrictively transmits the upper substrate 10 loaded with the color filters 12 to 14, thereby displaying a color image.
However, the combination of the electrophoretic film 30 and the upper substrate 10 with the lower substrate 50 (on which the lower electrodes 52 to 54 and the thin film transistors are formed) frequently generates an alignment defect in the electrophoretic display device of the related art. Also, since the incident light from the exterior via the color filter 12 to 14 passes through the color filter 12 to 14 again, the reflectivity of external light decreases due to a light leakage. Moreover, in the electrophoretic display device of the related art, the color characteristics of the color filters 12 to 14 deteriorate because of the heat-resistant quality of an adhesive used for combination.